As materials for embolizing blood vessels and the like for the purposes of hemostasis upon incision of an affected area, blocking the nutrient supply to a tumor, maintenance of the concentration of an anticancer drug in a tumor, etc., polymer particles such as cross-linked acrylic particles, degradable starch particles, poly(lactic acid/glycolic acid)copolymers (JP 05-000969 A) and block copolymers of polyethylene glycol and polylactic acid (JP 05-017245 B2, JP 2004-167229 A, JP 2005-312623 A and JP 2007-291323 A) are widely used. Among these, to tightly and securely embolizing blood vessels and the like, spherical polymer particles are preferably used.
The above-mentioned polymer particles can be delivered through a microcatheter or the like to the target site for vascular embolization, but they have problems such as insufficient flexibility and occurrence of aggregation to cause clogging of the catheter, and irreversible deformation of the polymer particles themselves before they reach the target site.
To solve these problems, control of the elasticity of the polymer particles by blending a plurality of types of polymers (JP 2007-145826 A), improvement in the ability to pass through a catheter by covering the surfaces of polymer particles with polyethylene glycol (JP 2007-146146 A), use of chemically cross-linked polymer particles (JP 2005-314535 A) and the like have been reported, and improved technologies have been developed.
However, although improvement in the problems of controlling the elasticity of polymer particles and the ability to pass through a catheter can be seen in the improved technologies such as blending of a plurality of types of polymers (JP '826), covering of the surfaces of polymer particles (JP '146) and use of chemically cross-linked polymer particles (JP 535), improvement in the problem of irreversible deformation of polymer particles themselves is insufficient. Hence, further improvement has been demanded to attain good embolization of blood vessels and the like. That is, development of an embolization material for blood vessels and the like wherein the ability of the polymer particles to recover their original shape after passing through a catheter (hereinafter referred to as “particle shape-recovering ability”) is enhanced is demanded.
Further, in improvement of a material for embolization of blood vessels and the like, conventional chemical cross-linking reactions to obtain chemically cross-linked spherical polymer particles require dispersion of a solution of a polymer or the like in a protic solvent such as water to form its droplets. However, since the protic solvent itself is involved in the chemical cross-linking reaction, control of the density of the chemical cross-links, and the like are very difficult, so that further improvement has been limited.
It could therefore be helpful to provide spherical biodegradable particles which have improved flexibility, cause less aggregation among particles, and have improved particle shape-recovering ability after passing through a catheter or the like, and a method of producing the particles.